1. Field of the Invention
This invention is generally directed to orthodontic brackets for use in aligning teeth and more specifically to self-ligating orthodontic brackets at least partially formed from shaped memory metallic alloys or non-metallic materials which include two pair of opposing tie wings which are spaced relative to one another along a base of each bracket and which serve to selectively and guidingly receive an archwire within archwire guide slots defined by each pair of opposing tie wings and posts.
2. Brief Description of Related Art
Generally, there are two basic styles of orthodontic brackets. A first style is known as a single wing wherein a pair of opposing elongated tie wings extend upwardly from a bracket base and are spaced to define an archwire guide slot therebetween. An example of a self-ligating single wing style bracket is disclosed in U.S. Pat. No. 6,663,385 to Tepper.
Twin brackets are the second style of brackets and have been developed to increase ease of bracket placement and use. Twin brackets include two pair of opposing tie wings which are spaced from one another with each pair defining an archwire guide slot therebetween. An example of such a bracket is described in U.S. Pat. No. 5,232,361 to Sachdeva et al. wherein the brackets are formed of titanium so as to be very hard and rigid. An example teaching away from a spaced pair of tie wings is disclosed in U.S. Pat. No. 5,356,289 to Watanabe wherein the brackets are formed of shape memory alloys or resins.
A variation of the twin bracket style has been developed to make the twin brackets self-ligating in order to avoid the necessity to tie-off the archwire used with the brackets. Such self-ligating twin brackets use supplemental hooks or latches which are mounted adjacent to each pair of tie wings for securely engaging or clamping an archwire. Unfortunately, the additional structure not only increases bracket costs and size, but also decreases bracket aesthetics and provides additional structure for trapping food and bacteria. An example of such a bracket is described in U.S. Pat. No. 6,554,612 to Georgakis et al.
Orthodontists are faced with many treatment difficulties as they bond orthodontic brackets to a patient's teeth and move them from crooked and irregular malocclusion positions to their ideal positions. The ideal alignment of teeth demands that they must be straight and aesthetical pleasing, but the teeth must also fit together correctly into normal occlusion and look and function in a superior clinical manner. There are a number of major challenges that Orthodontists must overcome to produce this superior clinical result.
There is often limited access to areas of the teeth where brackets must be placed to achieve normal orthodontic movement and produce superior treatment results. Useful areas may be small with access thereto very restricted, in which case, large brackets are not used successfully; whereas, smaller and compact twin type brackets can be placed in small areas and have enjoyed exceptional popularity among Orthodontists.
Ideal bracket placement on a patient's teeth is also necessary to produce ideal tooth alignment and achieve exceptional orthodontic results. To accomplish this necessary goal of ideal placement, brackets must often fit into small spaces between crooked and rotated teeth. A design feature of having a recessed point or horizontal groove located in the approximate center of the bracket will permit an Orthodontist to use a measuring device, such as a Boone Gauge, to precisely position brackets on teeth in exact desired positions.
Complete archwire engagement of the brackets on the teeth during various stages of orthodontic treatment is important but may not be possible. Many times, due to crooked alignment and closeness of the teeth, only two of the four bracket tie wings can be engaged at the same time. With single wing brackets or brackets without tie wings, it is extremely difficult to accomplish partial engagement successfully and this can result in an uncontrolled and unsatisfactory tooth movement. The true twin bracket design permits the engagement of at lease two of the opposing bracket tie wings to be used to begin tooth movement and, later in the treatment, two pair of opposing bracket tie wings can be used without compromising the patient's treatment.
The tooth movement process that is required to straighten teeth is very dynamic and constantly changing. The Orthodontist must have brackets that will accommodate the dynamics of tooth movement and not require replacement with new ones when a certain movement is required due to the difficulty of the patient's case.
Attachments such as Kobayashi hooks, metal ligatures, directional force elastics, elastomeric ties or elastomeric power chains are often used during various stages of orthodontic treatment. It is difficult to place such attachments on single wing style brackets and extremely difficult to place them on brackets without tie wings, however, a twin bracket configuration having four tie wings permits the Orthodontist to easily place such attachments and satisfactorily accomplish different aspects of a treatment.
Friction occurs as a normal part of tooth movement as a bracket and tooth slide along an archwire. This process is know as the sliding mechanics of orthodontics. The more points of contact between the archwire and a bracket slot during this process the greater the friction, which results in slower tooth movement and makes the treatment take longer. Elongated single wing brackets have increased friction resisting tooth movement and thus treatment is lengthy and more complicated to complete.
The aesthetic demands of the orthodontic patient are many and must be addressed to make the treatment acceptable to the patient. Smaller and less noticeable twin brackets are more aesthetic than larger single wing brackets and their aesthetics can be further improved. The true twin brackets allow the Orthodontists to attach colorful elastics, elastomeric ties, and power chain to the brackets that are pleasing to the patient.
A further major challenge to orthodontic treatment is the cleanliness of the brackets and areas where they are bonded or banded to the teeth. It is difficult for patients to clean areas adjacent to brackets and tooth surfaces. Bracket elements function as plaque traps that increase the chance of permanent stains, tooth decay, and gum disease. The use of larger single wings brackets makes it much harder for patients to keep their braces clean. The smaller twin designs are much easier for patients to clean and thus greatly reduced trapped food and are less likely to cause stains, tooth decay, or gum disease.
During the course of orthodontic treatment, archwires are placed and removed from the bracket/bracket slot as a normal part of treatment. Since most orthodontic brackets are made of stainless steel, both the bracket and bracket slots are rigid and inflexible. Once the archwire is placed in the bracket slot, it must be tied or ligated in place to prevent the archwire from coming out of the bracket and injuring the patient. The process of tying and untying every bracket to secure the archwire is a tedious and laborious procedure that must be repeated each time a new archwire is placed or removed. This process is time consuming and uncomfortable for the patient and inefficient for the Orthodontist. Self-ligating brackets have the advantage of using various mechanisms to secure archwires in the bracket slots without the need for metal or elastic ligatures. Because the current self-ligating brackets are not a true twin bracket design, they have serious limitations such that they are bulky and cumbersome to use in the small confines of the oral cavity.
In the 1980's nickel-titanium was introduced to orthodontics in the form of archwires with the trademark name of Nitinol™. The flexibility, shape memory effect, and superelasticity of Nitinol™ archwires offered a new wire that could be deflected to engage misaligned teeth and would return to its original form thereby straightening the teeth. The flexibility, shape memory effect, and superelastic nickel-titanium material has not, however, been used to construct a true twin bracket that looks and is shaped like the traditional stainless steel twin brackets.